I also heard the plastic stuff was pricey. Plus, I live where I need to consider I may have ice packing in on the "roof", if water drips down from the deck. Plus2, I wanted something to do a lot of work once and be done.

Here are pics. As I mentioned, I wanted the boards that the metal roof panels attached to oriented in the direction water flows. So, I used 2x4's, 2x2's etc between the deck joists and hanging down to set up the pitch. You can see each "row" hung further down as it got away from the house.

Next, I screwed long 2x2's to these, resulting in 2x2's the same direction as the joists with proper spacing to screw the roof panels to. You may be able to just screw a 2x4 to the side of a joist at the proper pitch, but I couldn't get the spacing right for screwing the bolts on, and I wanted them spaced equally for looks.

Because the deck cantilevers out over the steel beam (I added that too - went from 6 deck posts to two...), I had to pitch to the beam from both sides. Then had gutters added.

Overall, happy with the job, and the cost was <$500 I think. Deck is about 10x24 or so.

Here are a few pictures. The pic from the inside looking out shows the only spot that has a slow drip due to the curvature I made. That curve prevents me (6'4") from slicing my head on galvanized metal with a high point of about 6' at the gutter and a low point of 5' near the house. The metal does reflect light pretty well, and doesn't create the creepy cave effect that I thought would spook my kids. They're all comfortable playing in there.

The best advise I can give:

Don't try using a sawsall, get a metal blade for your circular saw

Don't do this in February like I did when it was sunny but 18 degrees. Leather gloves don't flex much when it's that cold.